java agent 使用及实现代码

agent

  package com.xueyou.demo.agent;

   import javassist.classpool;

   import javassist.ctclass;

   import javassist.ctmethod;

   import javassist.ctnewmethod;

   import java.lang.instrument.classfiletransformer;

   import java.lang.instrument.illegalclassformatexception;

   import java.security.protectiondomain;

   public class firstagent implements classfiletransformer {

     public final string injectedclassname = "com.xueyou.agentdemo.app" ;

     public final string methodname = "hello" ;

     public byte [] transform(classloader loader, string classname, class <?> classbeingredefined, protectiondomain protectiondomain, byte [] classfilebuffer) throws illegalclassformatexception {

       classname = classname.replace( "/" , "." );

   //    system.out.println(classname);

       if (classname.equals(injectedclassname)) {

         ctclass ctclass = null ;

         try {

           ctclass = classpool.getdefault().get(classname); // 使用全称,用于取得字节码类<使用javassist>

           ctmethod ctmethod = ctclass.getdeclaredmethod(methodname); // 得到这方法实例

           ctmethod.insertbefore( "system.out.println(11111111);" );

           return ctclass.tobytecode();

         } catch (exception e) {

           system.out.println(e.getmessage());

           e.printstacktrace();

         }

       }

       return null ;

     }

   }

package com.xueyou.demo;

import com.xueyou.demo.agent.firstagent;

import java.lang.instrument.instrumentation;

/**

  * hello world!

  */

public class app {

   public static void premain(string agentops, instrumentation inst) {

     system.out.println( "=========premain方法执行========" );

     system.out.println(agentops);

     // 添加transformer

     inst.addtransformer( new firstagent());

   }

}

<build>

     <plugins>

       <plugin>

         <groupid>org.apache.maven.plugins</groupid>

         <artifactid>maven-compiler-plugin</artifactid>

         <configuration>

           <source> 1.8 </source>

           <target> 1.8 </target>

           <encoding>utf- 8 </encoding>

         </configuration>

       </plugin>

       <plugin>

         <groupid>org.apache.maven.plugins</groupid>

         <artifactid>maven-shade-plugin</artifactid>

         <version> 3.0 . 0 </version>

         <executions>

           <execution>

             <phase> package </phase>

             <goals>

               <goal>shade</goal>

             </goals>

             <configuration>

               <transformers>

                 <transformer

                     implementation= "org.apache.maven.plugins.shade.resource.manifestresourcetransformer" >

                   <manifestentries>

                     <premainclass>com.xueyou.demo.app</premain- class >

                   </manifestentries>

                 </transformer>

               </transformers>

             </configuration>

           </execution>

         </executions>

       </plugin>

     </plugins>

   </build>